In many electrophotographic printers, corona chargers are used to impart a charge to a photoconductive film which is subsequently passed to an imaging section, a developing section and an image transfer section where the image on the photoconductor surface is transferred to a paper to produce a copy of the image on the paper. The paper is subsequently passed to a fuser section where a toner image on the paper is fixed to the paper by elevated temperature and pressure in the fuser section. The photoconductive film then passes through a neutralization section and thereafter past a brush cleaner which removes contaminants from the photoconductive film prior to passing the photoconductor film back to the primary charging section.
Often such corona chargers make byproducts including heat, ozone and nitrous oxides and many electrophotographic printers provide air flow systems to help evacuate these byproducts from a region that is proximate to the corona charger.
However, electrophotographic processes can create a wide variety of airborne contaminants. These contaminants can include, but are not limited to, substances such as fuser oil, toner, toner dust particles, addenda, paper fragments and the like. These contaminants can react in the highly reactive plasma atmosphere surrounding the wires that form the corona charger and coat the corona charger thereby creating localized regions that interfere with the formation of a charging field. This can result in non-uniform charge deposition on a primary imaging member such as a photoreceptor. The non-uniform charging can create artifacts in the formation of an electrostatic latent image that will then be reflected as defects in the developed visible toner image. Other examples of such contaminants include particulate contaminants such as a airborne toner dust, carrier particles, paper dust, dust from the abrasion of machine components, and can also include vapor contamination including silicon oils vaporized by a fuser and acidic byproducts caused by the operation of the corona charger.
As is shown, for example, in U.S. Pat. No. 5,424,540, “Corona Charger Wire Tensioning Mechanism” issued Jun. 13, 1995 to Garcia, et al and U.S. Pat. No. 6,038,120, “AC Corona Charger With Buried Floor Electrode” issued Mar. 14, 2000 to May, et al., corona chargers typically include bare corona wires which are located between a grid electrode and a shield. These wires are relatively small in diameter and since they are highly charged, contact between these wires and such contaminants can create charger arcing or other conditions that can cause machine errors, create non-uniform charging or reduce charger life. Contaminants also present a hazard to the primary imaging member either by becoming directly entrained in the primary imaging member or by remaining on the primary imaging member and being introduced into other subsystems to cause damage to such subsystems.
Accordingly, in an electrophotographic printer, air flow intended to remove the byproducts of corona charge creation can cause such contaminants to impact against corona wires and/or the surface of the electrostatic imaging member. Examples of such systems include, U.S. Pat. No. 5,132,731 to Oda, which describes an image forming apparatus including a pair of guide plates below developing units and adjacent to a transfer portion, the transfer portion including a transfer charger and a separating charger each of which has a first slit to form first paths and each of the guide plates having at least one second slit to form a second path. The image forming apparatus further includes a suction fan so as to suck gas generated in the transfer portion through the first paths and atmosphere around developing device through the second path. However, it will be appreciated that this approach creates a suction that can drive contaminants so that they are entrained in a corona wire or a photoconductor.
U.S. Pat. No. 5,128,720 issued to Creveling on Jul. 7, 1992 describes another approach to removing such gases. In this patent, a collection device is provided for collecting contamination product and harmful gasses from the corona charger. The collection device comprises a duct located within the shell of the charger closely adjacent to the walls thereof. The duct defines a series of ports spaced along the duct in the longitudinal direction of the charger shell. A flow of air into the duct is provided to directly collect such gasses from the environment within the reproduction apparatus without allowing such contamination products to contact and contaminate the corona wire and shell.
Another approach to the control of such contamination is the control of the flow of such contamination from the sources of the contamination. This requires very close control of the environment around substantially every operating system in the electrophotographic printer and is not considered feasible.
Nevertheless, it is necessary that air around a corona charger be replaced relatively frequently.